It is often desired to transfer energy to or from a rotating shaft. One method of doing so is with various types of energy converters. These energy converters are typically hydraulic or pneumatic rotary machines having either radial or axial pistons. The energy converter may also be an electric motor/generator. In any event the energy converter has the ability to allow the user to selectively draw energy from or supply energy to the rotating shaft from an energy reservoir.
Energy converters are often used in regenerative kinetic energy systems for vehicles. These systems typically interrupt the power flow from the engine to the wheels using a variety of clutches and hydraulic, pneumatic or electric motors. Therefore, the prior art energy converter transmissions introduce increased transmission losses even when the engine is driving the wheels directly since true direct drive is not possible.
One type of rotary machine commonly used has radial pistons and can be used as either a motor or a pump. The fluid flow between the radially extending cylinders is often provided through a pintal type valve which is essentially a hollow shaft with two or more ports for intermittent communication with passageways to the various cylinders. See, for example, U.S. Pat. Nos. 1,302,709 to Ragot, et al. and 2,163,080 to Benedek. One problem with pintal valves is that as the surfaces wear, the fit becomes looser and the valves tend to leak. Therefore rotary machines having pintal valves are generally disfavored for use with high pressures, such as are encountered in regenerative drive systems, because of a short life.
In order to overcome the disadvantage of the pintal valves in rotary machines, face valves have been used by some. In face valves the valves' mating surfaces are typically flat and define a plane perpendicular to the axis of rotation of the rotor of the machine. If wear occurs, one or both of the two members can be biased to take up the slack so that leaks are minimized. See U.S. Pat. Nos. 2,525,498 to Naylor et al. and 3,122,971 to Russell. However the Naylor patent is directed to a machine having only two openings in its fluid distribution plate; the axial forces therefore will not be balanced so that early failure of the machine may occur. Russell is a fixed displacement type of machine in which in order to reverse the direction of rotation, it is necessary to reverse the direction of flow of the fluid.
An aspect of rotary machines which should be recognized is that the driving interface between the motor and pistons is along the side of the cylinder walls. When acting as a rotary motor, the pistons drive the rotor by pressing on the cylinder walls with their sides; when the machine is acting as a pump the cylinder walls of the rotor press on the sides of the pistons. In either case it is desireable that the pistons be substantially enclosed or supported over their entire strokes to reduce force concentrations. However, this factor perhaps has not been fully appreciated in the prior art designs. See, for example, U.S. Pat. Nos. 2,189,773 to Benedek and 2,303,685 to Eden et al.
Other features of rotary machines disclosed in the prior art include eliptical tracks shown in U.S. Pat. No. 3,123,013 to Ganahl; the patent to Eden discloses a machine having means for inversely varying speed and torque and having the ability to reverse the direction of rotation by reversing the flow of the fluid; the device disclosed in the patent to Ragot can change the direction of rotation by changing the relative orientation of the ports.